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Here's an update on the project:
We ultimately decided to go with the solar option. 2x Renogy 200W rigid panels, 2x Victron SmartSolar 75/15 MPPT, and the Victron smart battery monitor. The Victron products network together for synchronized charging. I turned off the shore charger and switched to solar around 7pm Wednesday. We were still registering about 25W from each panel that late in the day! I left the boat with the fridge running for the (warm) night and when I returned to the boat after work yesterday (Thursday) around 4:00pm I was pleased to see that the batteries were charged. Looking at the trends, it looked like we were fully charged at approximately 12:50pm. We had plenty of extra capacity to operate the inverter/TV, fans, instruments, and radio until about 6pm when we started to pull from the batteries a little. It was a sunny day but I was very impressed with how well it worked. Stay tuned for results in different cloud conditions.

The electrical portion of the project was extremely easy and I found the Victron products and configuration process to be quick and intuitive. All I have left now is to finish securing the cables and install panel disconnects. For now I unplug the MC4 connectors when I switch to shore power.

The challenging part was designing the panel support to mount to the existing Bimini frame. It was very difficult to accurately measure and 3D model the frame because level, plumb, and flat don't exist on a boat! I ended up putting enough adjustability into the design to make it work. It's all made from 1" black StarBoard and 1.5x1.5x.125 aluminum angle. I'll be making an additional bimini frame support for both sides just aft of the winches for high wind/stormy situations.

I'll keep the two sensors in my cart then. It looks like Rod (Mainesail) still had a couple dozen as of 6 weeks ago. I sent an email this morning inquiring. I'll let everyone know what I hear.

Based on everyone's very helpful feedback, we're planning on starting with the L-N 105A alternator / Balmar regulator setup. I'm hoping I'll be able to snag one of the last remaining ER kits. I'll be sure to reverse engineer the cast cover and work on finding a manufacturing source for the future. Solar will probably have to wait until next year.

pbyrne- That is great information. Thank you. I know there are a number of ways I could make the fridge more efficient. I need to start by making sure it's charged to the proper pressures. It would help to have a way to circulate air in there too. I recall maybe seeing that someone did this in the past? When the fridge is full, everything on top freezes and everything on the bottom is warm. Definitely room for improvement. I like the portable fan idea to reduce battery use at night. Most of our lights, including anchor light are LED. I've been changing them to LED as we go. Lastly, yes, "analysis paralysis". My wife tells me she's sick of hearing me talk about this and to just order something already!

Jon W - That too is helpful info. Also thank you for the detailed write-up on your electrical upgrades in the wiki.

Noah - It's all sitting in my Amazon cart, almost ready for a tap on the expensive yellow button!

General remaining questions:

With the 105A alternator and Balmar regulator, how critical is the alternator temp and/or battery temp sensor?

Will the regulator get confused when the ACR kicks in and the start battery begins charging?

If not all parts for the alternator change-out can be sourced, what other alternator options are there?

Thanks everyone!

I have this one and have used it on both a 9.9 Evinrude and 3.5 Mercury. It seems to do the job just fine!

https://defender.com/en_us/c-level-universal-easylift-motor-tote-8877

Noah- My original Hella fans each draw .15A on low and .25A on high. On a warm night, we'd be running three of them (one in each sleeping area) on high. I put the lights on there for one hour as reference. My lights are powered from the house bank so they aren't charging while the engine is running with my current setup.

Jon- I added a picture of what I estimate I would get out of 400W of panels on an average August day. A state average for MI isn't very useful because we sometimes don't see the sun for the entire month of January. All that matters is May-Sept. There's a fantastic website that will generate a .CSV file for every hour of every day for a year for a specific location:

https://pvwatts.nrel.gov/

The estimator on Victron's website was very close but only has daily averages by month.

Ron,

It looks like you have a little bit of everything! How big are your solar panels?

I like your idea for adding extra insulation to the box. What did you use on the outside? With three sons that eat pretty much constantly it will be hard to keep the fridge lid closed. Thankfully they aren't quite big enough yet to lift the lid and get food out themselves! I suggested to my wife that we pre-make some meals and deep freeze them before we leave. We'd probably only get 2-3 days of refrigeration assistance from that before they'd be consumed though! For reference, my spreadsheet has refrigeration 75-80 amps/day.

I added a picture of my cheap power monitor and itemized power usage in 24hrs.

This topic has been covered many times over the years but in my opinion, technology, prices, knowledge, and parts availability changes frequently so it's worth a revisit.

Fast forward through a Michigan winter and here I am again trying to figure out an additional way to charge our 470Ah (4x GC2) lead acid house bank so we aren't tied to being plugged in at a marina every night.

Currently the original 51A alternator charges the dedicated group 27 engine battery only. The battery charger charges the house bank when on shore power. There is a combiner switch that will connect the engine battery and house bank but I've never attempted to use it. Last summer I installed much-needed fusing and purchased and installed an ACR but after reading multiple posts about frying original alternators charging the 4x golf cart banks like mine, I didn't make the final ACR connections.

We mostly day sail but we would like to take a two week trip go "up north" as we say in Michigan. It's usually difficult to get last-minute transient slip reservations to work around weather and lake conditions so having the ability to anchor for as much as three nights is a must.

Based on my extensive 72-hour energy budget spreadsheet, I estimate 120-150Ah use in a 24 hour period with the fridge mostly empty. With our family of five, the fridge will be completely full so there's a possibility my estimate could be low. (My estimate comes from watching trends on my cheap $20 voltmeter/watt counter and shunt combo from Amazon.) That puts us at 50% SOC sometime during the second night, assuming our batteries are actually relatively healthy. To get amps back in the bank, I see four options:

1. Utilize existing alternator but closely monitor SOC to stay above an unknown threshold that the alternator can handle.
2. Upgrade alternator to 90A or 105A with external smart regulator.
3. Add 2x 200W rigid solar panels on a frame above the bimini. I figure this is about the maximum I could reasonably add.
4. Bring our 3500W generator along. It's noisy, smelly and I don't know where we'd put it or the gasoline but we'd have battery charging, air conditioning, and the kids would have TV.

With options 1, 2, or 3, the big unknown for me is the math of the charging sequence for deep cycle batteries. This is especially true with the solar option where the available amps varies by time of day. I've read (a few times) the thread about battery acceptance but I'm still not clear on the math behind it. Google wasn't much help either. There's lots of information out there about discharging but not much on what's actually happening in the three charging states and what the ideals are.

Reference screenshots of the spreadsheet show two days based on leaving the dock in the morning on day 1 100% charged. One column shows estimated available amp hours without solar and one shows estimated available amp hours with solar and 80% charging efficiency.

Here's an excellent thread on alternators for this type of house bank: https://c34.org/bbs/index.php/topic,9773.0.html

After looking at Navpod prices, I opted to design something custom for our Vulcan 7. It allows easy access to the cables and the entire Vulcan unit can be removed without tools in seconds for safe storage. As a bonus, it gave me a place to add much-needed cupholders for all five of us. A local sheet metal company manufactured the two SS brackets for me ($50ea). Aside from hardware, the rest of the material is Starboard from the scrap bin at work. If your electronics don't require a sealed enclosure on the back side, something like this is fairly simple and could be made with router templates if you don't have access to a CNC router.

I purchased two deep 1 1/8" sockets and for the price of some donuts for my amazing and talented coworkers, one of our machinists machined off the top of the lower socket and one of our welders welded the two together.

Ron,
The 6AWG was already there from a PO. I'll add 4AWG to the list of future upgrades. From what I've read,  the OE alternator (8EM2017KA) has its own regulator built in.

Ron, the alternator output currently goes directly to the start battery via a 6AWG wire.

Ron, if my boat had ever had an ammeter, it's long gone!

KWKloeber-

I re-read the harness page on the C30 site and it makes sense now. I pulled the panel last night and took a good look at how everything is wired. Thankfully, the most critical hazards were already corrected by previous owners. The original wire harness connectors have been replaced by terminal strips and are no longer in service. There is definitely still room for improvement and I will work my way through the list of recommended wiring changes. My wiring matches the diagram here, except I have an extra wire on the key switch 'I' terminal for the fuel pump.
https://www.catalinadirect.com/images/features/Z4644%20Wiring%20Diagram.pdf

The yellow wire pictured is a jumper from the AO to alternator sense.

I hadn't considered what would happen if my house bank ended up being completely run down. It's true that I would lose fuel pump, glow, starting solenoid, etc.

Assuming the panel feed is left on the start battery and the AO goes to the house battery, will there be issues with the alternator excite or AC output to the tach? Or are those all electrically isolated within the alternator? If those are isolated, then maybe this is a non-issue. I'd see my starting battery voltage (when not combined) rather than monitoring the alternator, but maybe that's okay with me.

Thanks again to all of you for walking through this with me.

Stu - You are correct- I do have a voltmeter instead of an ammeter. Everything else in the M25XP manual diagram matches what I have except I don't have the orange-red wire between the alternator and starter. Were you able to get the full images to load? If not, I will try posting them again.

KWKloeber - Is the purpose of adding the negative wire to the alternator to add redundancy in case the negative wire to the engine comes loose? The way I envision the ACR working is this: Everything except the starter is powered by the house bank. Charging sources charge the house bank. When the start button is pressed, the Start Isolation (connected to the yellow/red wire) momentarily removes the path between the house bank and start battery so 100% of the starting effort comes from the starting battery. If I leave the smaller red wire on the main starter post (B post?), the cockpit voltmeter would be reading the voltage from the starting battery rather than the alternator/house battery while the batteries are not being combined by the ACR.

Regardless of where that red #5 wire ends up connecting to, I will definitely fuse it!

After reading through an incredible amount of information and wiring diagrams here, I was feeling fairly confident adding an ACR and fuses (we had neither). The one thing that has me stumped is the smaller red wire on the starter (+) post that feeds the cockpit engine panel. I haven't seen this one mentioned before. Should this wire get moved over to the alternator post so it is being fed from the house battery instead of the start battery? Thanks!